To determine whether H5N1 viruses could
be transmitted between humans, my team generated viruses that combined
the H5 haemagglutinin (HA) gene with the remaining genes from a
pandemic 2009 H1N1 influenza virus. Avian H5N1 and human pandemic 2009
viruses readily exchange genes in experimental settings, and those from
a human virus may facilitate replication in mammals. Indeed, we
identified a mutant H5 HA/2009 virus that spread between infected and
uninfected ferrets (used as models to study the transmission of
influenza in mammals) in separate cages via respiratory droplets in the
air. Thus viruses possessing an H5 HA protein can transmit between
mammals.

The above comments
by Yoshihiro Kawaoka indicate H5 can transmit in ferrets when
constructed on an H1N1pdm09 genetic background, raising concerns that
H5 transmission in humans can arrise through multiple mechanisms.
Since the paper at Nature has been censored, it is unclear if only one
combination has been tried, but the finding highlights the need for
additional studies.

In 2011 the addition of the H1N1pdm09 M gene onto H3N2v genetic
backgrounds has generated 12 human isolates including clusters in Iowa
and West
Virginia, raising concerns that this one gene on an H5N1 background
could lead to more efficient transmission.

Moreover, the recently released H5N1 sequences
from Egypt have recombined H1N1pdm09 sequences in PB1
and PB2
raising concerns that such acquisitions can lead to more efficient
transmission also, although the absence of sequences from any human
isolate in Egypt since March, 2010 and the absence of internal gene
sequences in earlier isolates limits conclusions.

The comments above make it clear that the full sequences from human
cases in Egypt should be released by NAMRU-3 and/or the US CDC
immediately, and the censored papers at Science and Nature should also
be published in full immediately.